gccrs: cleanup our enum type layout to be closer to rustc

This changes our enum type layout so for example:

  enum Foo {
      A,
      B,
      C(char),
      D { x: i32, y: i32 },
  }

Used to get layed out like this in gccrs:

  union {
    struct A { int RUST$ENUM$DISR; };
    struct B { int RUST$ENUM$DISR; };
    struct C { int RUST$ENUM$DISR; char __0; };
    struct D { int RUST$ENUM$DISR; i64 x; i64 y; };
  }

This has some issues notably with the constexpr because this is just a
giant union it means its not simple to constify what enum variant we are
looking at because the discriminant is a mess.

This now gets layed out as:

  struct {
     int RUST$ENUM$DISR;
     union {
         struct A { };
         struct B { };
         struct C { char __0; };
         struct D { i64 x; i64 y; };
     } payload;
  }

This layout is much cleaner and allows for our constexpr to work properly.

gcc/rust/ChangeLog:

	* backend/rust-compile-expr.cc (CompileExpr::visit): new layout
	* backend/rust-compile-pattern.cc (CompilePatternCheckExpr::visit): likewise
	(CompilePatternBindings::visit): likewise
	* backend/rust-compile-resolve-path.cc: likewise
	* backend/rust-compile-type.cc (TyTyResolveCompile::visit): implement new layout
	* rust-gcc.cc (constructor_expression): get rid of useless assert

Signed-off-by: Philip Herron <herron.philip@googlemail.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/gcc/rust/rust-gcc.cc b/gcc/rust/rust-gcc.cc
index 3f8986e..1efd872 100644
--- a/gcc/rust/rust-gcc.cc
+++ b/gcc/rust/rust-gcc.cc
@@ -1352,7 +1352,7 @@ constructor_expression (tree type_tree, bool is_variant,
 	      if (!TREE_CONSTANT (elt->value))
 		is_constant = false;
 	    }
-	  gcc_assert (field == NULL_TREE);
+	  // gcc_assert (field == NULL_TREE);
 	}
     }